Why do I hear a groaning noise when I start my car and then leave for work in the morning?

On models with a compact anti-lock brake system (ABS) unit, the vehicle's ABS emits a brief grunt or groan when it does a self-check. The self-check occurs when a vehicle is backed up or driven forward after being started. The groaning noise associated with the ABS self-check is a normal characteristic; it doesn't mean there is a problem with the ABS.